In a geothermal turbine plant, when the state of hot water or steam of a geothermal well corresponding to a steam supply source changes, a main steam pressure after flashing the steam or the hot water supplied from the geothermal well varies. Therefore, it is necessary to adjust the pressure of the steam to be supplied to the steam turbine so as to be a predetermined pressure in accordance with the main steam pressure.
In the nozzle governing type geothermal turbine according to Patent Literatures 1 and 2 below, the inside of an annular steam chest provided with the first stage nozzle is partitioned by a plurality of partition walls into one main steam chest with large capacity and one or a plurality of sub-steam chests with small capacity, and the one sub-steam chest or the plurality of sub-steam chests can be opened or closed individually. A steam chest connection pipe that supplies steam to the sub-steam chest is branched from a main steam pipe that supplies steam to the main steam chest, and the steam with the same pressure is supplied to the main steam chest and the sub-steam chest.
In the techniques according to Patent Literatures 1 and 2, when the output of the turbine has dropped to cause the sub-steam chest to operate, the first stage nozzle of the main steam chest where the impurities are deposited has the smaller opening area, and the first stage nozzle of the sub-steam chest where the impurities are not deposited has the large opening area. When the steam with the same pressure is supplied to the first stage nozzle in the main steam chest and the sub-steam chest with the different opening areas, the amount of steam (the pressure of steam) to flow from only the sub-steam chest into the initial-stage turbine is increased.
In the technique described in Patent Literatures 1 and 2, the uniform steam supply along the circumferential direction of the initial-stage turbine may fail. Therefore, in view of this, Patent Literature 3 below discloses the technique in which the steam can be supplied uniformly along the circumferential direction of the initial-stage turbine from both the first stage nozzle of the main steam chest and the sub-steam chest when the sub-steam chest is in operation.